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Abstract:

A non-aqueous electrolyte secondary battery has a positive electrode
containing a positive electrode active material, a negative electrode
containing a negative electrode active material, and a non-aqueous
electrolyte. The positive electrode active material includes a
lithium-nickel-manganese composite oxide having a hexagonal layered
rock-salt structure that belongs to the space group R-3m, and contains
lithium in 3b sites that contain transition metals. The
lithium-nickel-manganese composite oxide is represented by the molecular
formula Li[LixNiyMn2Mb]O2-a, where:
0.2<x<0.4, 0.12<y<0.5, 0.3<z<0.62, and
0≦a<0.5; M is at least one of Mg, Al, Zr, Ti, Nb, W, and Mo;
and variables x, y, z, and b satisfy the expressions x>(1-2y)/3,
1/4≦y/z≦1.0, 0<b/(y+z)≦0.1, and
1.0≦x+y+z+b≦1.1.

Claims:

1. A non-aqueous electrolyte secondary battery comprising: a positive
electrode containing a positive electrode active material; a negative
electrode containing a negative electrode active material; and a
non-aqueous electrolyte, wherein the positive electrode active material
comprises a lithium-nickel-manganese composite oxide having a hexagonal
layered rock-salt structure that belongs to the space group R-3m and
containing lithium in 3b sites that contain transition metals, the
lithium-nickel-manganese composite oxide being represented by the
molecular formula Li[LixNiyMn.sub.zMb]O2-a where:
0.2<x<0.4, 0.12<y<0.5, 0.3<z<0.62, and
0.ltoreq.a<0.5; M is at least one element selected from the group
consisting of Mg, Al, Zr, Ti, Nb, W, and Mo; and the variables x, y, z,
and b satisfy the expressions x>(1-2y)/3, 1/4.ltoreq.y/z≦1.0,
0<b/(y+z)≦0.1, and 1.0.ltoreq.x+y+z+b≦1.1.

2. The non-aqueous electrolyte secondary battery according to claim 1,
wherein the capacity ratio of the negative electrode to the positive
electrode (negative electrode charge capacity/positive electrode charge
capacity) is 1.0 or greater when the battery is charged until the
potential of the positive electrode reaches 4.45 V (vs. Li/Li.sup.+) or
higher.

Description:

[0001] This application is a divisional application of Ser. No.
13/067,095, filed May 6, 2011, which is a divisional application of Ser.
No. 11/703,831, filed Feb. 8, 2007, which claims priority based on
Japanese Patent Application Nos. 2006-031166 and 2006-093957, filed Feb.
8, 2006, and Mar. 30, 2006, respectively, and which are incorporated
herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to non-aqueous electrolyte secondary
batteries that use as a positive electrode active material a
lithium-containing transition metal oxide containing nickel and manganese
as transition metals.

[0004] 2. Description of Related Art

[0005] In recent years, development of HEVs (Hybrid Electric Vehicles),
which use electric motors in conjunction with automobile gasoline
engines, has been in progress worldwide in order to resolve the
environmental issues caused by vehicle emissions. Nickel-hydrogen
secondary batteries have conventionally been used as power sources for
the HEVs, but lithium-ion secondary batteries have been expected to be
applied as HEV power sources because of their higher voltage and
capacity.

[0006] One of the important issues relating to a lithium-ion secondary
battery for HEV applications is to reduce the costs. Lithium-ion
secondary batteries that have already been commercially available for
power supply applications of portable electronic devices such as mobile
telephones, camcorders, and notebook computers generally use a composite
oxide containing Co as the positive electrode active material. However,
because of cost considerations, positive electrode materials that do not
contain costly metal elements such as Co are desirable for the
large-sized lithium-ion secondary batteries for HEVs. For HEV
applications, higher input power is preferable from the viewpoint of
system design particularly for the purpose of efficient battery
regeneration. Accordingly, a battery with low charge-discharge voltage is
needed, and in addition, a battery that achieves a good balance between
input power and output power is desirable. In particular, in HEV
applications, not all the capacity range of the battery is evenly used
but the charge range in the vicinity of 50% SOC is mainly used.
Therefore, the design requirements are that the battery should have low
charge-discharge voltages in that range and exhibits a good balance
between input power and output power.

[0007] A problem with conventionally used active materials, such as
lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2),
lithium-manganese oxide (LiMn2O4), and Li--Ni--Co--Mn composite
oxide, is, however, that these materials cause the positive electrode
potential to be high, and thus lead to high battery voltage, resulting in
low input power. In view of such circumstances, a low-cost, low-voltage
lithium-ion secondary battery designed to exhibit excellent power
characteristics is sought after for HEN applications.

[0008] In recent years, active materials that are made of only elements
that can be obtained at relatively low cost, such as lithium-containing
olivine-type phosphate and Ni--Mn-based composite oxide, have been
investigated widely as positive electrode to materials for lithium-ion
secondary batteries for HEV applications that can meet the
above-mentioned requirements. Among them, a Li(Li--Ni--Mn) composite
oxide having a crystal structure that belongs to the space group R-3m and
containing lithium at the transition metal site enables the
charge-discharge potential at 50% is SOC to be about 100 mV to 200 mV
lower than those of the above-described positive electrode materials that
have already been in commercial use, because lithium extraction from the
3b sites occurs during an initial charge at 4.45 V (vs. Li/Li.sup.+) or
higher and, after this reaction, the capacity originating from the
oxidation-reduction reaction of Mn3+/Mn4+ is obtained at 3.5 V
(vs. Li/Li.sup.+) or lower. Because of these properties, the
Li(Li--Ni--Mn) composite oxide has drawn attention as a promising
positive electrode material that achieves high capacity and higher input
power at low cost. (See, for example, U.S. Patent Application Publication
No. 2003/0108793A1).

[0009] Nevertheless, the Li(Li--Ni--Mn) composite oxide disclosed in the
just-mentioned publication shows a high irreversible capacity during the
initial charge, so the initial charge-discharge efficiency of the
positive electrode active material is poor. This necessitates excessive
use of the negative electrode active material in the battery design,
which leads to problems such as a low battery capacity and poor load
characteristics.

BRIEF SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a non-aqueous
electrolyte secondary battery that uses, as its positive electrode active
material, a lithium-transition metal composite oxide containing nickel
and manganese as transition metals, such that the battery achieves a good
balance between input power and output power, exhibits excellent power
characteristics, and moreover has a high initial charge-discharge
efficiency and a high discharge capacity.

[0012] According to the present invention, the positive electrode active
material comprises the lithium-nickel--manganese composite oxide having a
hexagonal layered rock-salt structure that belongs to the space group
R-3m and containing lithium in the 3b sites that contain the transition
metals, and the lithium-nickel-manganese composite oxide is represented
by the molecular formula described above. The use of this positive
electrode active material makes it possible to provide a non-aqueous
electrolyte secondary battery that achieves a good balance between input
power and output power, exhibits excellent power characteristics, and
moreover has high initial charge-discharge efficiency and a high
discharge capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a three-phase diagram illustrating the composition region
of Li--Ni--Mn in the lithium-nickel-manganese composite oxide according
to the present invention;

[0014]FIG. 2 is a graph illustrating the initial charge-discharge
efficiencies of Examples according to the present invention;

[0015]FIG. 3 is a graph illustrating the discharge capacities of Examples
according to the present invention;

[0016]FIG. 4 is a graph illustrating the input/output power ratios of
Examples according to the present invention;

[0017]FIG. 5 is a graph illustrating the input I-V resistances of
Examples according to the present invention;

[0018]FIG. 6 is a graph illustrating the output I-V resistances of
Examples according to the present invention; and

[0020] A non-aqueous electrolyte secondary battery according to the
present invention comprises a positive electrode containing a positive
electrode active material, a negative electrode containing a negative
electrode active material, and a non-aqueous electrolyte. The positive
electrode active material comprises a lithium-nickel-manganese composite
oxide having a hexagonal layered rock-salt structure that belongs to the
space group R-3m and containing lithium in 3b sites that contain
transition metals. The lithium-nickel-manganese composite oxide is
represented by the molecular formula
Li[LixNiyMn.sub.z]O2-a where: 0<x<0.4,
0.12<y<0.5, 0.3<z<0.62, and 0≦a<0.5; and the
variables x, y, and z satisfy the expressions x>(1-2y)/3,
1/4≦y/z≦1.0, and x+y+z=1.0.

[0021] In the present invention, the lithium-nickel-manganese composite
oxide containing lithium in 3b sites and being represented by the
above-specified compositional formula is used as the positive electrode
active material. The use of such a lithium-nickel-manganese composite
oxide as the positive electrode active material makes it possible to
provide a non-aqueous electrolyte secondary battery that achieves a good
balance between input power and output power, exhibits excellent power
characteristics, and moreover has high initial charge-discharge
efficiency and a high discharge capacity.

[0022] In the lithium-nickel-manganese composite oxide
Li[LixNiyMn2]O2-a of the present invention, the
variable x, which represents the amount of Li contained in the 3b sites
containing the transition metals, is within the range 0<x<0.4; the
variable y, which represents the amount of Ni in the
lithium-nickel-manganese composite oxide, is within the range
0.12<y<0.5; the variable z, which represents the amount of Mn in
the lithium-nickel-manganese composite oxide, is within the range
0.3<z<0.62; the variable a, which represents the amount of oxygen
defects, is within the range 0≦a<0.5; and the variables x, y,
and z satisfy the expressions x>(1-2y)/3, 1/4≦y/z≦1.0,
and x+y+z=1.0. When the variables x, y, z, and a are within the
just-described ranges and the variables x, y, and z satisfy the
just-described expressions, the battery exhibits higher initial
charge-discharge efficiency and higher discharge capacity and achieves
better regenerative power characteristics than batteries using
conventional lithium-nickel--manganese composite oxides.

[0023] In particular, it is preferable that the variables x, y, and z be
within the following ranges 0.2<x<0.4, 0.3<y<0.4,
0.4<z<0.62, and 1/4≦y/z≦1/2, from the viewpoint of
increasing the amount of lithium that is extracted from the 3b sites
during the initial charge and widening the redox region for Mn4+/3+,
so as to lower the charge-discharge potentials, for the purpose of
enhancing the regenerative power characteristics.

[0024] The lithium-nickel-manganese composite oxide of the present
invention may further contain at least one metal element M having a
valency of from 2 to 6. Specifically, the lithium-nickel-manganese
composite oxide may further contain, for example, B, Mg, Al, Si, P, Ca,
Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Ge, As, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh,
Pd, In, Sn, Sb, Te, Ba, a lanthanoide element, Hf, Ta, W, Re, Os, Ir, Pt,
Pb, Bi, Ra, and an actinoid element. It is preferable that the mole ratio
of the added metal element M be 0.1 or less with respect to the
transition metal elements contained in the transition metal sites 3b, and
more preferably from 0.001 to 0.05. Accordingly, in accordance with
another aspect, the present invention provides a non-aqueous electrolyte
secondary battery comprising a positive electrode containing a positive
electrode active material, a negative electrode containing a negative
electrode active material, and a non-aqueous electrolyte, wherein the
positive electrode active material comprises a lithium-nickel-manganese
composite oxide having a hexagonal layered rock-salt structure that
belongs to the space group R-3m and containing lithium in the 3b sites
containing transition metals, the lithium-nickel-manganese composite
oxide being represented by the molecular formula
Li[LixNiyMn.sub.zMb]O2-a where: 0<x<0.4,
0.12<y<0.5, 0.3<z<0.62, and 0≦a<0.5; M is at least
at least one metal element having a valency of from 2 to 6; and the
variables x, y, z, and b satisfy the expressions x>(1-2y)/3,
1/4≦y/z≦1.0, 0<b/(y+z)≦0.1, and
1.0≦x+y+z+b≦1.1.

[0025] It is particularly preferable that the metal element M in the
molecular formula be at least one element selected from the group
consisting of Mg, Al, Zr, Ti, Nb, W, and Mo.

[0026] In the lithium-nickel-manganese composite oxide having a hexagonal
layered rock-salt structure that belongs to the space group R-3m and
containing lithium in 3b sites that contain transition metals, and being
represented by the molecular formula
Li[LixNiyMn2]O2-a according to the present invention,
it is preferable that the amount of lithium in the 3b sites be determined
using an x-ray diffraction analysis or a neutron diffraction analysis. In
this case, the advantageous effects of the present invention can be
obtained also when the crystal structure belongs to P3112, other
than R-3m, since Meng and others advocate that Mn surrounds Li when Li
occupies the 3b site and reported that the space group is restored at P3,
12 from R-3m (Y. S. Meng, G. Ceder, C. P. Grey, W. S. Yoon and Y.
Shao-Horn, Electrochem. and Solid-State Lett., Volume 7, Issue 6,
previously presented. A155-A158 (2004)).

[0027] In the non-aqueous electrolyte secondary battery of the present
invention, it is preferable that the capacity ratio of the negative
electrode to the positive electrode (negative electrode charge
capacity/positive electrode charge capacity) is 1.0 or greater when the
battery is charged until the potential of the positive electrode reaches
4.45 V (vs. Li/Li.sup.+ or higher, and more preferably, the capacity
ratio is within the range of from 1.0 to 1.2. That is, it is preferable
that the non-aqueous electrolyte secondary battery of the present
invention be charged until the potential of the positive electrode
reaches 4.45 V (vs. Li/Li.sup.+) or higher when used. Therefore, when a
carbon material such as graphite is used as the negative electrode active
material, it is preferable that the end-of-charge voltage of the battery
be set at 4.35 V or higher. It is more preferable that the battery be
charged until the potential of the positive electrode reaches 4.45 V to
4.80 V (vs. Li/Li.sup.+). Accordingly, when a carbon material is used as
the negative electrode active material, it is preferable that the
end-of--charge voltage be set at a voltage of from 4.35 V to 4.70 V.

[0028] In the present invention, the solute of the non-aqueous electrolyte
may be any lithium salt that is generally used as a solute in non-aqueous
electrolyte secondary batteries. Examples of the lithium salt include
LiPF6, LiBF4, LiCF3SO3, LiN(CF3SO2)2,
LiN(C2F5SO2)2, LiN(CF3SO2)
(C4F9SO2), LiC(CF3SO2)3,
LiC(C2F5SO2)3, LiAsF6, LiClO4,
Li2B10Cl10, Li2B12Cl12, and mixtures
thereof. In addition to these salts, the non-aqueous electrolyte may
contain a lithium salt having an oxalato complex as anions, and more
preferably, the non-aqueous electrolyte may contain
lithium-bis(oxalato)borate.

[0029] The solvent of the non-aqueous electrolyte used in the present
invention may be any solvent that has conventionally been used as a
solvent for an electrolyte in non-aqueous electrolyte secondary
batteries. Examples of the solvent include: cyclic carbonates, such as
ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene
carbonate; and chain carbonates, such as dimethyl carbonate, methylethyl
carbonate, and diethyl carbonate. Particularly preferable is a mixed
solvent of a cyclic carbonate and a chain carbonate.

[0030] Although the negative electrode active material is not particularly
limited in the present invention, it is preferable that the negative
electrode active material be a carbon material in which the lithium
intercalation and deintercalation associated with charge-discharge
operations are reversibly performed.

EXAMPLES

[0031] Hereinbelow, the present invention is described in further detail
based on examples thereof. It should be understood, however, that the
present invention is not limited to the following examples but various
changes and modifications are possible without departing from the scope
of the invention.

Example 1

Preparation of Positive Electrode Active Material

[0032] A Li(LiNiMn)O2 composite oxide was prepared in the following
manner. A 1M sodium hydroxide solution was added to an aqueous solution
of 0.5M nickel acetate and 1.0M manganese acetate so that hydroxides of
Ni and Mn were coprecipitated, to obtain a composite hydroxide of Ni and
Mn. Using the composite hydroxide thus obtained, Li2CO3 and the
Ni--Mn composite hydroxide were mixed so that the mole ratio of the
elements Li:Ni:Mn became 1.20:0.27:0.53. The resultant mixture was
pre-sintered in an air atmosphere at 500° C. for 10 hours and
thereafter sintered at 1000° C. for 20 hours, to thus obtain the
Li(LiNiMn)O2 composite oxide. The resultant Li(LiNiMn)O2
composite oxide had a composition of
Li[Li0.20Ni0.27Mn0.53]O2.

Preparation of Positive Electrode

[0033] A positive electrode was prepared in the following manner. The
positive electrode active material prepared in the just-described manner
was mixed with acetylene black as a conductive agent and an
N-methyl-2-pyrrolidone solution in which polyvinylidene fluoride as a
binder agent was dissolved so that the weight ratio of the positive
electrode active material and the conductive agent and the binder agent
became 90:5:5, and the mixture was then kneaded to prepare a positive
electrode slurry. The resultant slurry was applied onto an aluminum foil
serving as a current collector and thereafter dried. Thereafter, the
resultant material was pressure-rolled using pressure rollers, and a
current collector tab was attached thereto, whereby the positive
electrode was prepared.

Preparation of Electrolyte Solution

[0034] An electrolyte solution was prepared in the following manner.
LiPF6 as a solute was dissolved in a solvent of a 3:3:4 volume ratio
mixture of ethylene carbonate -(EC), methyl ethyl carbonate (MEC), and
dimethyl carbonate (DMC) at a concentration of 1 mole/liter, and 1 weight
% of vinylene carbonate (VC) was further dissolved therein as a
surface-film forming agent.

Preparation of Three-electrode Beaker Cell

[0035] Using the positive electrode and the electrolyte solution prepared
in the above-described manner, a three-electrode beaker cell as
illustrated in FIG. 7 was prepared in a glove box under an argon
atmosphere. As illustrated in FIG. 7, an electrolyte solution 4 was
filled in the beaker, and a working electrode 1, a counter electrode 2,
and a reference electrode 3 were put in the electrolyte solution 4. The
foregoing positive electrode was used as the working electrode 1, and
metallic lithium was used for the counter electrode 2 and the reference
electrode 3 to prepare the cell 1.

Charge-Discharge Test

[0036] At room temperature, the cell was charged at 1 mA to 4.6 V (vs.
Li/Li.sup.+), then rested for 10 minutes, and thereafter discharged at 1
mA to 2.0 V (vs. Li/Li.sup.+). The charge-discharge efficiency in this
cycle was defined as the initial charge-discharge efficiency, and the
measurements of the initial charge-discharge efficiency and the discharge
capacity were obtained.

I-V Resistance Measurement Test

[0037] The input I-V resistance of the cell was determined by the
following test.

[0042] The above charge-discharge tests 1) to 4) were conducted
sequentially at room temperature. The potential of the cell was measured
10 seconds after each of the charging operations. I-V resistance was
determined from the slope of the measured potential values versus the
current values, and open circuit potential (OCP) was found from the
intercepts.

[0043] From the obtained I-V resistance and OCP, an input power value was
calculated using the following equation.

Input power (W)=(4300-OCP)/I-V resistance×4300

[0044] The output I-V resistance was determined by the following test.

[0049] The above charge-discharge tests 1) to 4) were conducted
sequentially at room temperature. The potential of the cell was measured
10 seconds after each of the charging operations. The I-V resistance was
determined from the slope of the measured potential values versus the
current values, and the OCP was found from the intercepts.

[0050] From the obtained I-V resistance and OCP, an output power value was
calculated using the following equation.

Output power (W)=(OCP-2000)/I-V resistance×2000

[0051] Using the charge and output power values calculated from the above
equations, an input/output power ratio of the cell was calculated
according to the following equation.

Input/output power ratio=Input power/Output power

Example 2

[0052] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.30:0.35:0.35, and thus,
Li[Li0.30Ni0.35Mn0.35]O2 was obtained. Subsequently,
using the positive electrode active material thus prepared, a
three-electrode beaker cell 2 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 3

[0053] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.30:0.30:0.40; and thus,
Li[Li0.30Ni0.30Mn0.40]O2 was obtained. Subsequently,
using the positive electrode active material thus prepared, a
three-electrode beaker cell 3 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 4

[0054] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.30:0.23:0.47, and thus, Li
[Li0.30Ni0.23Mn0.47]O2 was obtained. Subsequently,
using the positive electrode active material thus prepared, a
three-electrode beaker cell 4 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 5

[0055] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.30:0.18:0.52, and thus,
Li[Li0.30Ni0.18Mn0.52]O2 was obtained. Subsequently,
using the positive electrode active material thus prepared, a
three-electrode beaker cell 5 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 6

[0056] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.30:0.14:0.56, and thus,
Li[Li0.30Ni0.14Mn0.56]O2 was obtained. Subsequently,
using the positive electrode active material thus prepared, a
three-electrode beaker cell 6 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 7

[0057] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and 4MgCO3Mg(OH)25H2O were
mixed so that the mole ratio of the elements Li:Ni:Mn:Mg became
1.3:0.23:0.47:0.0035, and thus,
Li[Li0.30Ni0.23Mn0.47Mg0.0035]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 7 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 8

[0058] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and 4MgCO3Mg(OH)25H2O were
mixed so that the mole ratio of the elements Li:Ni:Mn:Mg became
1.3:0.23:0.47:0.007, and thus,
Li[Li0.30Ni0.23Mn0.47Mg0.007]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 8 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 9

[0059] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and 4MgCO3Mg(OH)25H2O were
mixed so that the mole ratio of the elements Li:Ni:Mn:Mg became
1.3:0.23:0.47:0.014, and thus,
Li[Li0.30Ni0.23Mn0.47Mg0.014]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 9 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 10

[0060] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and Al(OH)3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Al became 1.3:0.23:0.47:0.0035, and thus,
Li[Li0.30Ni0.23Mn0.47Al0.0035]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 10 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 11

[0061] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and Al(OH)3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Al became 1.3:0.23:0.47:0.007, and thus,
Li[Li0.30Ni0.23Mn0.47Al0.007]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 11 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 12

[0062] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and Al(OH)3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Al became 1.3:0.23:0.47:0.014, and thus,
Li[Li0.30Ni0.23M0.47Al0.014]O2 was
obtained. Subsequently, using the positive electrode active material thus
prepared, a three-electrode beaker cell 12 was fabricated in the same
manner as described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 13

[0063] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and ZrO2 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Zr became 1.3:0.23:0.47:0.0035, and thus,
Li[Li0.30Ni0.23Mn0.47Zr0.0035]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 13 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 14

[0064] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and ZrO2 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Zr became 1.3:0.23:0.47:0.007, and thus,
Li[Li0.30Ni0.23Mn0.47Zr0.007]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 14 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 15

[0065] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and ZrO2 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Zr became 1.3:0.23:0.47:0.014, and thus,
Li[Li0.30Ni0.23Mn0.47Zr0.014]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 15 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 16

[0066] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and TiO2 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Ti became 1.3:0.23:0.47:0.0035, and thus,
Li[Li0.30Ni0.23Mn0.47Ti0.0035]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 16 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 17

[0067] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and TiO2 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Ti became 1.3:0.23:0.47:0.007, and thus,
Li[Li0.30Ni0.23Mn0.47Ti0.007]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 17 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 18

[0068] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and TiO2 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Ti became 1.3:0.23:0.47:0.014, and thus,
Li[Li0.30Ni0.23Mn0.47Ti0.014]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 18 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 19

[0069] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and Nb2O5 were mixed so that the
mole ratio of the elements Li:Ni:Mn:Nb became 1.3:0.23:0.47:0.0035, and
thus, Li[Li0.30Ni0.23Mn0.47Nb0.0035]O2 was
obtained. Subsequently, using the positive electrode active material thus
prepared, a three-electrode beaker cell 19 was fabricated in the same
manner as described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 20

[0070] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and Nb2O5 were mixed so that the
mole ratio of the elements Li:Ni:Mn:Nb became 1.3:0.23:0.47:0.007, and
thus, Li[Li0.30Ni0.23Mn0.47Nb0.007]O2 was
obtained. Subsequently, using the positive electrode active material thus
prepared, a three-electrode beaker cell 20 was fabricated in the same
manner as described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 21

[0071] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and Nb2O5 were mixed so that the
mole ratio of the elements Li:Ni:Mn:Nb became 1.3:0.23:0.47:0.014, and
thus, Li[Li0.30Ni0.23Mn0.47Nb0.014]O2 was
obtained. Subsequently, using the positive electrode active material thus
prepared, a three-electrode beaker cell 21 was fabricated in the same
manner as described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 22

[0072] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and WO3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:W became 1.3:0.23:0.47:0.0035, and thus,
Li[Li0.30Ni0.23Mn0.47W0.0035]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 22 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 23

[0073] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and WO3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:W became 1.3:0.23:0.47:0.007, and thus,
Li[Li0.30Ni0.23Mn0.47W0.007]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 23 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 24

[0074] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and WO3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:W became 1.3:0.23:0.47:0.014, and thus,
Li[Li0.30Ni0.23Mn0.47W0.014]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 24 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 25

[0075] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and MoO3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Mo became 1.3:0.23:0.47:0.0035, and thus,
Li[Li0.30Ni0.23Mn0.47Mo0.0035]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 25 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 26

[0076] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and MoO3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Mo became 1.3:0.23:0.47:0.007, and thus,
Li[Li0.30Ni0.23Mn0.47Mo0.007]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 26 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Example 27

[0077] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that Li2CO3, the
Ni--Mn composite hydroxide, and MoO3 were mixed so that the mole
ratio of the elements Li:Ni:Mn:Mo became 1.3:0.23:0.47:0.014, and thus,
Li[Li0.30Ni0.23Mn0.47Mo0.014]O2 was obtained.
Subsequently, using the positive electrode active material thus prepared,
a three-electrode beaker cell 27 was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Comparative Example 1

[0078] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.40:0.20:0.40, and thus,
Li[Li0.40Ni0.20Mn0.40]O2 was obtained. Subsequently,
using the positive electrode active material thus prepared, a
three-electrode beaker cell A was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Comparative Example 2

[0079] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.40:0.15:0.45, and thus, Li
[Li0.40Ni0.15Mn0.45]O2 was obtained. Subsequently,
using the positive electrode active material thus prepared, a
three-electrode beaker cell B was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

Comparative Example 3

[0080] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.00:0.50:0.50, and thus,
Li[Ni0.50Mn0.50]O2 was obtained. Subsequently, using the
positive electrode active material thus prepared, a three-electrode
beaker cell C was fabricated in the same manner as described in Example
1, and using the resultant cell, the charge-discharge tests were
conducted to obtain test results.

Comparative Example 4

[0081] A positive electrode active material was prepared in a similar
manner to that described in Example 1, except that the Li2CO3
and the Ni--Mn composite hydroxide were mixed so that the mole ratio of
the elements Li:Ni:Mn became 1.07:0.40:0.53, and thus,
Li[Li0.07Ni0.40Mn0.53]O2 was obtained. Subsequently,
using the positive electrode active material thus prepared, a
three-electrode beaker cell D was fabricated in the same manner as
described in Example 1, and using the resultant cell, the
charge-discharge tests were conducted to obtain test results.

[0082] The results of the initial charge-discharge efficiency measurements
and discharge capacity measurements for the cells 1-6 of Examples 1-6 and
the cells A-D of Comparative Examples 1-4 are shown in Table 1 below.

[0083] The results of the input I-V resistance, output I-V resistance, and
input/output power ratio measurements for the cell 4 of Example 4 and the
cells 7-27 of Examples 7-27 are shown in Table 2 below.

[0084] The initial charge-discharge efficiencies of the cells 1-6 as well
as the cells A, B, and D are shown in FIG. 2, and the discharge
capacities of the cells 1-6 and the cells A-D are shown in FIG. 3,
respectively.

[0085] The results shown in Table 1 and FIGS. 2 and 3 clearly demonstrate
that the cells 1-6 of Examples 1-6, each of which employed the
lithium-nickel-manganese composite oxide having a composition according
to the present invention as the positive electrode active material,
achieved superior initial charge-discharge efficiencies and discharge
capacities than the cells A-D of Comparative Examples 1-4.

[0086] FIG. 1 shows a Li--Ni--Mn three-phase diagram illustrating the
lithium-nickel-manganese composite oxides of the cells 1-6 of Examples
1-6 as well as the cells A-D of Comparative Examples 1-4. The
lithium-nickel-manganese composite oxide of the present invention has a
composition defined by the region bounded by the four straight lines
x=0.4, x=(1-2y)/3, y/z=1/4, and y/z=1/1 (not including any composition
that falls on the lines x=0.4 and x=(1-2y)/3).

[0087] By comparing the Example cells 1-6 with the Comparative Example
cell D, which uses the conventional lithium-nickel-manganese composite
oxide reported in U.S. Patent Application Publication No. 2003/0108793A1,
it has been shown that the initial charge-discharge efficiency and the
discharge capacity are improved by the compositions in which the amount x
of lithium contained in the 3b sites that contain transition metals is
greater than (1-2y)/3, in other words, under the condition x>(1-2y)/3.

[0088] Moreover, by comparing the Example cells 1-6 with the Comparative
Example cells A and B, in which the amount x of the lithium is 0.4, it
has been shown that the initial charge-discharge efficiency and the
discharge capacity are poor when the amount of the lithium is 0.4.
Therefore, according to the present invention, it has been shown that the
amount x of Li in the 3b sites that contain the transition metals should
be less than 0.4.

[0089] Furthermore, as is clear from the comparison between the cells 1 to
6 of Examples and the cell C of Comparative Example, it has been shown
that the effect of improving the discharge capacity as achieved by the
present invention cannot be obtained when Li is not contained in the 3b
sites that contain the transition metals.

[0090] In the present invention, the advantageous effect is especially
evident when utilizing the capacity range of Mn4+/3+ after the
lithium extraction from the 3b sites. Accordingly, it is more
advantageous when the amount z of Mn is larger than the amount y of Ni.
Nevertheless, if the amount of Mn is too large, irreversible capacity
increases, and the initial charge-discharge efficiency reduces.
Therefore, it is preferable that the ratio y/z of Ni/Mn be less than 1
but greater than 1/4.

[0091] As clearly seen from the results shown in Table 2 and FIG. 4, the
cells 7-27 of Examples 7-27 according to the present invention, each of
which uses as the positive electrode active material a
lithium-nickel-manganese composite oxide that contains at least one metal
element having a valency of from 2 to 6, exhibit input/output power
ratios that are closer to 1 than the input/output power ratio of the cell
4 of Example 4, which does not contain the additive metal element. Thus,
the cells 7-27 of Examples 7-27 provide improvements in the balance
between input power and output power.

[0092] Moreover, as clearly seen from the results shown in Table 2 and
FIGS. 5 and 6, the cells 13-27 of Examples 13-27, each of which uses as
the positive electrode active material a lithium-nickel-manganese
composite oxide that contains at least one metal element having a valency
of from 4 to 6, exhibit considerably lower input I-V resistances and
output I-V resistances than that of the cell 4 of Example 4, which does
not contain the additive metal element and than those of the cells 7-12
of Examples 7-12, which contain at least one metal element having a
valency of from 2 to 3.

[0093] It is believed that the reason why the use of the above-specified
lithium-nickel-manganese composite oxide according to the present
invention achieves excellent initial charge-discharge efficiency and
discharge capacity is as follows, although the details are not yet clear.
It is believed that, in each of the conventional lithium-nickel-manganese
composite oxides xLi[Ni0.5Mn0.5]O2+(1-x)Li2MnO3
and Li[Li.sub.(1-2y)/3NixMn.sub.(2-x)/3])2, the valencies of the Ni
and the Mn in a completely discharged state are exclusively 2 and 4,
respectively, and almost no oxygen holes are present. In the composition
of the present invention, for example, in the case of
Li[Li0.30Ni0.30Mn0.40]O2 of the cell 3, it is
understood that electroneutrality cannot be maintained if the valencies
of Ni and Mn are 2 and 4, respectively. Even if Ni is oxidized to a
valency of 3, electroneutrality is not reached. Also, it is not believed
that the valency of Mn is in an oxidation state higher than a valency of
4 at 4.6 V (vs. Li/Li.sup.+ in the initial charge. Accordingly,
electroneutrality is maintained because of oxygen defects even before the
battery is subjected to the initial charge, and as a result, the
electrochemical irreversible capacity produced during the initial charge
is small. It is believed that the initial charge-discharge efficiency is
improved in this way. Also, the reason why the discharge capacity becomes
higher than that of the conventional active materials at that time is
believed to be as follows, although the details are not yet clear. Since
the lithium-nickel-manganese composite oxide of the invention contains Li
excessively, the extraction of Li from the 3a sites is easier than the
conventional composition xLi[Ni0.5Mn0.5]O2+(1-x)
Li2MnO3 that is represented as a solid solution of
Li[Ni0.5Mn0.5]O2 and Li2MnO3, and as a result, a
larger capacity of Mn4+/3+ can be obtained at a discharge process
after the initial charging.

[0094] It is believed that the reason why the power balance between input
power and output power is improved according to the present invention by
adding at least one metal element having a valency of from 2 to 6 to the
above-specified lithium-nickel-manganese composite oxide is as follows,
although the details are not yet clear. In order to improve the power
balance between input power and output power, it is necessary to reduce
the OCP. In order to reduce the OCP at 50% SOC with the
lithium-nickel-manganese composite oxide of the present invention, the
capacity of Mn4+/3+ produced through the extraction of lithium from
the 3b sites during the initial charge should be increased relative to
the total capacity. It is believed that the added metal element according
to the present invention exists without being involved in the
charge-discharge processes, but the presence of such a metal element in
the vicinity of the nickel and manganese, which are involved in
charge-discharge processes, is believed to influence the electronic
state. For example, when a metal element having a valency of 3 is added
to the lithium-nickel-manganese composite oxide, the valency of the
nickel, which is believed to have been 2 in a discharged state, is
shifted to a valency greater than 2 due to the influence from the nearby
metal element whereas the valency of the manganese, which is believed to
have been 4 in a discharged state, is shifted to a valency lower than 4.
As a result, the proportion of the capacity originating from the redox
reaction of the nickel reduces, and on the contrary, the proportion of
the capacity originating from the redox reaction of the manganese
increases. Consequently, the OCP reduces. On the other hand, when a metal
element having a valency of 6 is added to the lithium-nickel-manganese
composite oxide, the valency of the nickel is increased to a valency
higher than 2 due to the influence from the nearby metal element, and the
valency of the manganese is also increased to a valency higher than 4.
Nevertheless, in the charge-discharge reactions of the present invention,
it is believed that the manganese does not undergo an oxidized reaction
such as to shift its valency from 4 to 5, and it is not involved in the
charge-discharge processes. As a result, only the capacity of the nickel
reduces, and the relative proportion of the capacity of the manganese
increases with respect to the total capacity. It is believed that, by
these processes, the addition of the metal element(s) to the
lithium-nickel-manganese composite oxide serves to reduce the OCP and to
improve the power balance between input power and output power.

[0095] In addition, it is believed that the reason why the input I-V
resistance and the output I-V resistance are reduced by adding, according
to the present invention, at least one metal element having a valency of
from 4 to 6 to the above-specified lithium-nickel-manganese composite
oxide is as follows, although the details are not yet clear. It is highly
likely that such a metal element having a valency of 4 or greater is
present outside the crystal lattice because the metal element is not
easily substituted for the nickel or manganese in the crystal.
Accordingly, it is believed that the addition of such an element having a
valency of 4 or greater inhibits the crystal growth during the calcining,
so the crystallite size tends to be small. As a result, the diffusion of
lithium inside the active material that is associated with
charge-discharge reactions becomes easier, and consequently the I-V
resistances reduce.

[0096] As has been described, the use of the Li(LiNiMn)O2 composite
oxide having a prescribed composition according to the present invention
as the positive electrode active material makes it possible to improve
the initial charge-discharge efficiency and discharge capacity and thus
to provide a battery that exhibits excellent regenerative power
characteristics.

[0097] Only selected embodiments have been chosen to illustrate the
present invention. To those skilled in the art, however, it will be
apparent from the foregoing disclosure that various changes and
modifications can be made herein without departing from the scope of the
invention as defined in the appended claims. Furthermore, the foregoing
description of the embodiments according to the present invention is
provided for illustration only, and is not intended to limit the
invention as defined by the appended claims and their equivalents.

[0098] This application claims priority of Japanese Patent Application
Nos. 2006-031166 and 2006-093957 filed Feb. 8, 2006 and Mar. 30, 2006,
respectively, each of which is incorporated herein by reference.

Patent applications by Hideki Kitao, Sakaiminato-City JP

Patent applications by Noriyuki Shimizu, Osaka JP

Patent applications by Yoshinori Kida, Osaka JP

Patent applications in class Nickel component is active material

Patent applications in all subclasses Nickel component is active material